Molybdenum disulphide

ABSTRACT

A PROCESS FOR THE REDUCTION OF THE CORROSIVITY OF OLEOPHILIC METAL SULPHIDES IN WHICH, EITHER DURING OR AFTER GRINDING OF A METAL DISULPHIDE IN AN ORGANIC GRINDING LIQUID, THE METAL SULPHIDE IS CONTACTED WITH ORGANIC BASES ESPECIALLY ORGANIC-AMINES.

United States Patent 3,647,689 MOLYBDENUM DISULPHIDE Aleksander Jerzy Groszek, London, England, assignor to The British Petroleum Company Limited, London, England No Drawing. Filed Sept. 24, 1969, Ser. No. 860,817 Claims priority, application Great Britain, Sept. 27, 1968, 45,973/68 Int. Cl. C10m 5/02 US. Cl. 252-25 3 Claims ABSTRACT OF THE DISCLOSURE A process for the reduction of the corrosivity of oleophilic metal sulphides in which, either during or after grinding of a metal disulphide in an organic grinding liquid, the metal sulphide is contacted with organic bases especially organic amines.

This invention relates to metal sulphides, more particularly it relates to oleophilic metal sulphides.

Oleophilic metal sulphides have a ratio of heat of adsorption of n-dotriacontane from n-heptane to heat of adsorption of n-butanol from n-heptane of at least 1:2 and preferably at least 1:1, and a surface area of at least square metres per gram.

The heats of adsorption can be measured using a flow micro-calorimeter as described in Chemistry and Industry, Mar. 20, 1965, pp. 482-485.

Oleophilic metal sulphides can be prepared by grinding a metal sulphide in an organic grinding liquid preferbly in the substantial absence of air, i.e., the metal sulfide is preferably below the surface of the organic liquid throughout the grinding operation. This method of preparing oleophilic metal sulphides is described in UK. Pat. 1,162,223.

Satisfactory products can be obtained by grinding in most organic liquids, but it is desirable to use one the bulk of which can be easily removed from the oleophilic metal sulphide. Those liquids distilling below 500 C. and having a viscosity below 600 centistokes at 100 F. (38 C.) are therefore preferred. Liquids having a surface tension below 72 dynes/crn., preferably from 10 to 40 dynes/cm, at 25 C. are preferred. Liquids of viscosity less than 30 centistokes, preferably less than 3 centistokes and most preferably less than 1 centistoke are most suitable.

Suitable organic liquids are hydrocarbons, including straight-chain or branched-chain, saturated or unsaturated aliphatic, saturated or unsaturated, substituted or unsubstituted, cyclo-aliphatic, and substituted or unsubstituted aromatic compounds, preferably containing up to 10 carbon atoms. Examples of such compounds are n-heptane, octene-2,2,2,4-trimethylpentane, cyclohexane, benzene or toluene. Branched aliphatic compounds are particularly preferred. Other suitable organic liquids are those compounds which contain fluorine, chlorine, or phosphorus and chlorine, for example, carbon tetrachloride.

Other suitable organic liquids are the polar oxygen compounds such as isopropyl alcohol. Silicone fluids can also be used.

For best results, the amount of metal sulphide in the metal sulphide/ organic grinding liquid mixture should not exceed 50% wt.; preferably it should be from 2 to Wt.

The grinding may be carried out in any suitable grinding mill or device and it is desirable to continue the grinding until an oleophilic metal sulphide having a surface area (as determined by nitrogen adsorption) of from 10 to 400, preferably from 30 to 200, square metres per gram is obtained. Usually this can be achieved by grinding at normal temperatures for the required period but the temperature of the mixture may be artificially increased if desired, for example, up to 400 C. In this case, liquids which have viscosities up to 600 centistokes at F. (38 C.) may be used, for example, mineral lubricating oils, ranging from spindle oils to bright stocks.

One of the quickest and most effective techniques is to carry out the grinding in a vibratory ball mill.

Air should be excluded so far as possible during the grinding operation and this can be most easily achieved by filling the mill with the organic liquid first, followed by the balls and metal sulphide. A suitable procedure is to fill the mill with the liquid, add half the balls, then the metal sulphide and finally the rest of the balls.

When using a ball mill, it is of course desirable to use balls made of a material which does not react with the metal sulphide and which does not wear unduly during the grinding. Vibratory ball mills usually contain steel balls and these are suitable for the present purpose. It is preferred to use a hard grade of steel for the balls. Preferably vibratory ball mills with an amplitude of vibration of at least 2 mm. and a vibration frequency of 1500 cycles per minute are used.

A magnetic filter can be used to remove small steel particles from the slurry. A circulatory system can also be used wherein the slurry is pumped through an internal magnetic filter and then returned to the mill.

A suitable vibratory ball mill is sold under the trade name Magapact, manufactured by Pilamec Limited. The grinding effect is produced by the impact of the balls upon the metal sulphide and upon each other, and the casing.

The slurry of oleophilic metal sulphide can be sep arated from the balls by sieving or by displacement by another liquid and sieving.

It has been found that all forms of metal sulphides, are acidic to various extents, the acidity is confined to polar sites and is thought to arise from oxidation reactions.

As oleophilic metal sulphides are used as solid lubricants and lubricant additives their corrosive properties should be reduced as much as possible.

We have found that contacting the metal sulphide with a base, either during or after grinding, reduces the corrosive nature of the oleophilic metal sulphide.

According to the invention there is provided a method of providing an improved oleophilic metal sulphide which comprises grinding a metal disulphide in an organic liquid to a surface area of at least 10 square metres per gram and, either during or after grinding, contacting the metal sulphide with a base.

The grinding conditions which can be used in the present invention are those described above for the preparation of oleophilic metal sulphides.

The metal sulphides that can be used include molybdenum disulphide, tungsten disulphide, lead sulphides and tin sulphides. The preferred metal sulphide is molybdenum disulphide.

Any base can be used provided it is sufficiently basic to substantially neutralise the acidic entities present and it is not a base which is corrosive itself or which can adversely affect the nature of the oleophilic metal sulphide. The bases can be composed entirely of organic groups, or of metal atoms combined with one or more organic groups.

Suitable organic bases include the organic amines especially primary amines such as propylarnines, the butylamines, the hexylamines and alkyl substituted hexylamines. Bases containing metal groups combined with one or more organic groups such as zinc and alkaline earth metal carboxylates and phenates often possess desirable lubricating properties in themselves and these bases are especially useful.

When the base is contacted with the metal sulphide during the grinding operation then the grinding medium and base should be chosen so that the base is soluble in or miscible with the grinding medium.

When the base is contacted with the oleophilic metal sulphide and the base is not a liquid then it is preferably dissolved in an organic solvent. Suitable solvents are the aliphatic hydrocarbons and alcohols. After the treatment with the base the excess base can be removed using conventional techniques such as distillation or solvent extraction.

When the base is dissolved in the grinding medium amounts of 150% by weight and preferably 520% by weight are suitable.

Oleophilic metal sulphides have the property of thickening oils into greases and also possess better lubricating properties in dispersions than non-oleophilic metal sulphides. These applications of oleophilic metal sulphides are described in UK. Pat. 1,162,222.

Oleophilic molybdenum disulphide can be compressed into solid compacts as described in UK. patent application 38,979/67.

The invention is described in the following example.

EXAMPLE Two commercially available molybdenum disulphide powders of different purity (powders A and B of the table following) were ground in a Megapact vibratory ball mill made by Pilamec Limited. The grinding chamber was filled with n-heptane and the balls and molybdenum disulphide then added. The grinding chamber was then sealed. The amplitude of the vibration was 4 mm. and the frequency 3000 cycles per minute. The grinding was continued for 8 hours.

The powders produced were contacted with excess n-butylamine and the surplus n-butylamine removed.

The grinding was then repeated with the n-heptane containing 12% by weight of n-butylamine.

The powders produced were compressed at a pressure of 65,000 p.s.i.g. and the compacts formed tested on a pin and disc machine.

The wear value K is a measure of the corrosivity and abrasiveness of the compact, and as can be seen from the following table the contacting of the olephilic molybdenum disulphide with n-butylamine brings about a reduction of corrosivity of the molybdenum disulphide compact.

1. A method of preparing molybdenum disulphide which comprises grinding molybdenum disulphide in an organic liquid distilling below 500 C., having a surface tension less than 72 dynes/cm. at 25 C. and viscosity less than 600 centistokes at 100 F. having dissolved therein from 2 to 20% by weight of an organic amine, in the substantial exclusion of air till a surface area of at least 10 square metres per gram is attained, to obtain a dispersion of oleophilic molybdenum disulphide and removing the said organic liquid from the dispersion.

2. A method as claimed in claim 1 in which the organic amine is n-butylamine.

3. A method as claimed in claim 1 in which the organic liquid is a hydrocarbon having a viscosity of less than 3 centistokes at 100 F.

References Cited UNITED STATES PATENTS 6/1970 Cairns et a1. 25225 8/1970 Dodson et al. 252-25 US. Cl. X.R. 23134; 252 

